There are various types of luminaires which have been designed for a variety of special purposes, such as, for example, for mounting on poles to provide street or parking lot illumination, on a wall to provide a specific pattern of illumination adjacent the wall, or on a ceiling to provide either direct or indirect lighting. There are also some luminaires which are promoted as being for general purpose lighting, but the degree of flexibility in mounting and light directivity is usually limited, thereby limiting the usefulness thereof.
It is desirable to be able to support a general purpose luminaire at one mounting point because that permits the greatest flexibility as to the direction. However, mountings of known types which permit this form of support are not capable of holding a luminaire of significant weight at a selected angular adjustment under adverse conditions of wind and vibration, or are extremely complicated to adjust.